We are cloning a gene from an echinoderm that has the potential of representing the first long-term marker of calcium and neuronal activity. The gene encodes a protein that is responsible for the bioluminescence in certain species of brittlestars and has remarkable fluorescence properties. Only after calcium-triggered bioluminescence does this protein adopt a bright green fluorescence that persists indefinitely! The protein is present in nerves and it marks the active neurons in vivo for days after stimulated to produce luminescence and indefinitely if the tissue is fixed for histology. Like GFP, the fluorescence of this protein is intense and slow to bleach so it does not require low light level measurements. It has spectral properties very similar to GFP so that all of the resources developed for this standard can be used for ophiopsilin. Once cloned, we should be able to target the protein in any cell type of interest and examine the history of activity. Because virtually all cells use calcium signaling pathways it would serve as a universal indicator. Ideally suited for this type of approach are nerve, muscle and secretory cell types. It may be possible to use this indicator in the central nervous system to trace the circuitry at a single cell level. Thus, this calcium latch protein has the potential to revolutionize the manner in which we image the history of cellular activity in healthy and diseased tissue. Project Narrative We are exploiting the unique features of a naturally occurring calcium dependent fluorescence indicator in the neurons of echinoderms. The protein responsible for bioluminescence latches into a persistent GFP like fluorescence after binding calcium. As such it represents the first long-term marker of calcium and membrane activity. Because it is genetically coded it can be targeted for expression to any cell type and the fluorescence even persists through histology. As such it could be serve as a read out history of membrane activity and calcium signaling in healthy or diseased tissue. PUBLIC HEALTH RELEVANCE: We are exploiting the unique features of a naturally occurring calcium dependent fluorescence indicator in the neurons of echinoderms. The protein responsible for bioluminescence latches into a persistent GFP like fluorescence after binding calcium. As such it represents the first long-term marker of calcium and membrane activity. Because it is genetically coded it can be targeted for expression to any cell type and the fluorescence even persists through histology. As such it could be serve as a read out history of membrane activity and calcium signaling in healthy or diseased tissue.